Method of manufacturing a replica as well as a replica obtained by carrying out an UV light-initiated cationic polymerization

ABSTRACT

The invention relates to a method of manufacturing a replica, which method comprises the provision of a bondable resin composition between a mold and a substrate or a blank, carrying out a curing treatment and removing the replica thus manufactured from the mold, which replica comprises the substrate and the reproduction of the mold provided thereon. The invention further relates to a replica obtained by carrying out a UV light-initiated cationic polymerization.

[0001] The invention relates to a method of manufacturing a replica,which method comprises the provision of a bondable resin compositionbetween a mold and a substrate or a blank, carrying out a curingtreatment and removing the replica thus manufactured from the mold,which replica comprises the substrate and the reproduction of the moldprovided thereon. The invention also relates to a replica obtained bycarrying out a UV light-initiated cationic polymerization.

[0002] Such a method is known per se from U.S. Pat. No. 4,890,905, filedin the name of the current applicant. The replication process employs amold or a matrix having an accurately defined surface which is thenegative of the desired optical profile of the replica. In the exactdetermination of the definition of the surface of the mold or matrix,the shrinkage of the synthetic resin of the replica must be taken intoaccount. A small quantity of a liquid, curable synthetic resincomposition is provided on the surface of the mold. The substrate, whichmay or may not be transparent to UV light, is subsequently pressed withthe desired side against the mold, or conversely, as a result of whichthe synthetic resin spreads between the surface of the substrate and thesurface of the mold. Said liquid, synthetic resin composition may beprovided on the substrate instead of the mold. The synthetic resinmixture is cured and the substrate with the cured synthetic resin layerbonded thereto is removed from the mold. The free surface of thesynthetic resin layer is the negative of the corresponding surface ofthe mold. The advantage of the replication process is that opticalcomponents, such as lenses having a complicated refractive surface, forexample an aspherical surface, can be manufactured in a comparativelysimple manner without subjecting the substrate to complex polishingtreatments. A drawback of such a replication by means of polymerizationis the occurrence of shrinkage. Particularly if the flow of the bondableresin composition is impeded by gelation or a substantial increase inviscosity, further polymerization will lead to the development ofstresses or even to premature delamination. If the product issubsequently removed from the mold, as in the case of, in particular, areplication process, only a partial relaxation of the stresses takesplace, particularly if the product formed is composed of a denselybonded polymeric network. Such a bonded polymeric network is desired,however, for the cohesion of the product formed.

[0003] Therefore, it is an object of the invention to provide a bondableresin composition which, if it is cured against a mold, exhibits aslittle relaxation as possible after it has been removed from the moldand hence represents, as accurately as possible, the shape of the mold.

[0004] Another object of the invention is to provide a method enabling areplica layer to be provided, either simultaneously or successively, ontwo sides of the substrate.

[0005] Yet another object of the invention is to provide a method ofmanufacturing a replica, which method employs a bondable resincomposition which also features a high reaction rate and a reaction thatcan be controlled by UV radiation.

[0006] A still further object of the invention is to provide a method ofmanufacturing a replica, which method employs a bondable resincomposition, the final product of which corresponds to the currentlyapplicable quality requirements regarding transparency and hardness.

[0007] Another object of the invention is to provide a method ofmanufacturing a replica, wherein a bondable resin composition isemployed whose viscosity is so low that it can be accurately dosed inthe replica process without any problems

[0008] The method mentioned in the opening paragraph is characterized inaccordance with the invention in that the curing treatment is a UVlight-initiated cationic polymerization, the resin composition usedbeing a compound comprising at least two cationically polymerizablecyclic ether groups, which only shows signs of gelation when at least50% of the conversion that can be achieved in the mold under therelevant curing conditions has taken place.

[0009] By using such a bondable resin composition, the final productwill be free of shrinkage stresses owing to the late gelation andcomparatively small shrinkage. According to the applicant, thecomparatively small degree of shrinkage can be attributed to the factthat the ring-opening process on which the current curing treatment isbased does not cause new bonds, instead the number of bonds in thestarting product and in the bonded product more or less correspond toeach other, so that only a small degree of shrinkage takes place.Conversely, in the known (meth)acrylate compounds, as known from theabove-mentioned U.S. Pat. No. 4,890,905, an increase in the number ofnew bonds is brought about, which explains the high degree of shrinkage.In addition, in the compounds in accordance with the invention, gelationand vitrification do not occur until a high conversion percentage isreached, so that the development of stresses starts at a much laterstage. According to the current applicants, this surprising effect isbrought about by a surprisingly large degree of chain transfer, as aresult of which, at the beginning of the bonding reaction, predominantlycomparatively small molecules are formed which do not form a gel until ahigh conversion percentage is reached. If the method in accordance withthe invention is applied to replicate aspherical lenses of, for example,CD players, the application of the bondable composition in accordancewith the invention will cause the shape of the mold to correspondsubstantially exactly to the product finally formed, as a result ofwhich a much smaller shrinkage correction is necessary. As, in addition,after the product has been removed from the mold, less relaxation isnecessary, it is to be expected that the amount of spread in the shapeof the replicated lenses will be much smaller in the above-mentionedproduction process. The method in accordance with the invention canparticularly suitably be used to replicate relief structures requiringan accurate (sub-micron) shape reproduction.

[0010] Compounds which can suitably be used in the method in accordancewith the invention to manufacture a replica include a bondable resincomposition of the following general formula:

[0011] wherein:

[0012] Y=—O—, —SO₂—, —CH₂—, —C(CF₃)₂—, —C(CH₃)₂—,

[0013] X=a halogen or CH₃,

[0014] R₁=—CH₂—, —C(CH₃)₂—,

[0015] R₂=—OCH₂CH₂—, —OCCH₃HCH₂—, —OCH₂CCH₃H—, —OCH₂CHOHCH₂—,

[0016] R₃=H, C_(n)H_(2n+1),

[0017] n=an integer≧1,

[0018] p=1-4,

[0019] m, a, b, c are each individual integers in the range from 0-4.

[0020] For the bondable resin composition use can also suitably be madeof a compound selected from the group formed by 1,2,7,8-diepoxyoctane,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,bis(3,4-epoxycyclohexylmethyl)adipate,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate andC₁₂-C₁₄-alkylglycidylether and the corresponding oxetane compoundsthereof. An oxetane compound which can particularly suitably be used is1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene.

[0021] Dependent upon the viscosity of the selected bondable resincomposition, it may be preferred, in certain embodiments, that thebondable resin composition additionally comprises a reactive diluent,which is preferably selected from the group formed bybutylglycidylether, heptylglycidylether, octylglycidylether,allylglycidylether, p-t-butylphenylglycidylether, phenylglycidylether,cresylglycidylether, diglycidylether of 1,4-butanediol, diglycidyletherof neopentylglycol, diglycidylether of polypropeneglycol,vinylcyclohexanedioxide, diglycidylether of recorcinol, diglycidyletherof polypropeneglycol and diglycidylester of linoleic acid dimer and thecorresponding oxetane compounds thereof.

[0022] The invention further relates to a replica obtained by carryingout a UV light-initiated cationic polymerization of a compoundcomprising at least two cationically polymerizable cyclic ether groups,which compound does not exhibit gelation until at least 50% of theconversion that can be achieved in the mold under the relevant curingconditions has taken place, if necessary in the presence of a reactivediluent.

[0023] A suitable replica is any relief structure requiring an accurate(sub-micron) reproduction. A further example of a suitable replica is anoptical component, in particular an (a)spherical lens, a lens array, aprism, a grating or another relief structure for optical applications,or a combination thereof.

[0024] These and other aspects of the invention will be apparent fromand elucidated with reference to the embodiment(s) describedhereinafter.

COMPARATIVE EXAMPLE

[0025] An aspherical lens is manufactured by means of a commonly knownphotoreplication method by providing a reactive mixture comprising amonomer, a photoinitiator and, if necessary, a sensitizer on the convexside of a planospherical substrate, after which said substrate carryingthe reactive mixture is introduced into an aspherical mold and pressedsuch as to cause the liquid to spread between the substrate surface andthe mold surface without the inclusion of air bubbles. Subsequently, thesubstrate is exposed to UV light passing through said substrate andoriginating from a high-pressure mercury lamp provided with filterstransmitting only the spectral range from 320 to 390 nm. If necessary,the exposure process can be carried out such that the UV light alsopasses through the mold, provided said mold is embodied so as to betransparent. After the exposure process, the lens is removed from themold and optically and mechanically examined.

[0026] The above-mentioned photoreplication method is carried out usinga reactive mixture comprising a solution of 4%2,2-dimethyoxy-1,2-diphenylethane-1-on in2,2-bis(4-(2-methacryloxyeth-1-oxy)phenyl)propane. This mixture isexposed at room temperature for 7 seconds at an intensity of 40 mW/cm²and subsequently removed, whereafter it is re-exposed at 10 mW/cm² for 1hour at room temperature and stabilized in the dark for 16 hours at 140°C. The lens thus obtained is optically and mechanically characterized.

[0027] During the polymerization process, the mixture exhibitedapproximately 7% shrinkage. Using such a reactive mixture, theaspherical mold must be corrected in an iterative process in order toobtain a lens of the desired shape.

EXAMPLE IN ACCORDANCE WITH THE INVENTION

[0028] The commonly known photoreplication method described in thecomparative example hereinabove is used, except that the reactivemixture used is a solution of 4.75% diphenyliodoniumhexafluoroarsenateand 0.25% anthracene in 2,2-bis(4-(glycidyloxy)phenyl)propane. Thismixture is subsequently exposed at room temperature for 7 seconds at anintensity of 100 mW/cm² and subsequently removed, whereafter it isre-exposed at 10 mW/cm² for 1 hour at room temperature, and stabilizedin the dark at 120° C. for 16 hours. The lens thus obtained is opticallyand mechanically characterized.

[0029] During the polymerization process, the mixture exhibitedapproximately 2.3% shrinkage. Using such a reactive mixture comprising acompound including at least two cationically polymerizable cyclic ethergroups, it is not, or hardly, necessary, unlike the reactive mixtureused in the comparative example, to correct the aspherical mold in orderto obtain a lens of the desired shape. This favorable result isattributed to the fact that after removal from the mold, hardly anyrelaxation occurs. This very small degree of relaxation, as compared tothe reactive mixture used in the comparative example, can be attributed,according to the current applicants, to a combination of reducedshrinkage and retarded gelation.

1-5. (canceled).
 6. A replica obtained by carrying out a UVlight-initiated cationic polymerization of a compound comprising atleast two cationically polymerizable cyclic ether groups, which compoundonly exhibits gelation when at least 50% of the conversion that can beachieved in the mold under the relevant curing conditions has takenplace, if necessary in the presence of a reactive diluent.
 7. A replicaas claimed in claim 6, characterized in that this replica comprises arelief structure on at least one side, which relief structure must meethigh (sub-micron) requirements with a view to the necessary accuracy ofform.
 8. A replica as claimed in claim 6, characterized in that thereplica obtained is an optical component.
 9. A replica as claimed inclaim 8, characterized in that the optical component obtained is an (a)spherical lens, a lens array, a prism, a grating or another reliefstructure for optical applications, or a combination thereof.
 10. Areplica as claimed in claim 7, characterized in that the compound isrepresented by the following general formula I:

wherein: Y=—O—, —SO₂—, —CH₂—, —C(CF₃)₂—, —C(CH₃)₂—, X=a halogen or CH₃,R₁=—CH₂—, —C(CH₃)₂—, R₂=—OCH₂CH₂—, —OCCH₃HCH₂—, —OCH₂CCH₃H—,—OCH₂CHOHCH₂—,

R₃=H, C_(n)H_(2n+1), n=an integer≧1, p=1-4, m, a, b, c are eachindividual integers in the range from 0-4.
 11. A replica as claimed inclaim 8, characterized in that the compound is selected from the groupformed by 1,2,7,8-diepoxyoctane,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,bis(3,4-epoxycyclohexylmethyl)adipate,bis(3,4-epoxy-6-methylcyclohexyl-methyl)adipate andC12-C14-alkylglycidylether and the corresponding oxetane compoundsthereof, in particular1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene.
 12. A replica asclaimed in claim 9, characterized in that for the reactive diluent useis made of a compound selected from the group formed bybutylglycidylether, heptylglycidylether, octylglycidylether,allylglycidylether, p-t-butylphenylglycidylether, phenylglycidylether,cresylglycidylether, diglycidylether of 1,4-butanediol, diglycidyletherof neopentylglycol, diglycidylether of polypropeneglycol,vinylcyclohexanedioxide, diglycidylether of recorcinol, diglycidyletherof polypropeneglycol and diglycidylester of linoleic acid dimer and thecorresponding oxetane compounds thereof.